1. Field of Use
This invention relates generally to electronic control circuits for electric generators. In particular it relates such control circuit which connect and disconnect a generator to and from a load circuit in response to generator output voltage (or frequency) levels.
2. Description of the Prior Art
Many boats, such as small fishing vessels, cabin cruisers and some sailboats, use a gasoline or diesel powered adjustable speed internal combustion engine for propulsion and necessary speed changes of the boat are accomplished by changing the speed of the engine. As a practical matter, however, when the boat is underway, it and the engine are usually operated in a so-called "cruise speed" range for about 90% of the time. The electric power required to operate electrical equipment aboard such boats (i.e., lights, electronic and radio gear, refrigeration equipment, motors for pumps and winches, etc.) is usually supplied from a d.c. or a.c. (60 Hz, single phase) generator which, when driven at rated speed, provides a rated output voltage of 110 (or 220) volts, Usually it is more economical and conservative of space to use the boat propulsion engine to drive the generator than to use a separate smaller auxiliary engine. Depending on the particular installation, the generator can be coupled directly to a PTO shaft on the engine or connected thereto by a gear-type or V-belt drive. The drive components are, of course, selected and matched so that when the engine is being operated in the "cruise speed" range, the generator is driven at its rated speed range or thereabout and delivers rated voltage or thereabout. As a result of such arrangements, however, changes in engine speed result in corresponding changes in generator speed. As long as the engine is operated at in cruise speed range, generator output voltage is sufficient to meet normal laod requirements. However, if engine speed decreases or increases relative to the cruise spped range, generator output voltage (and frequency, if a.c.) correspondingly increases or decreases an may drop below minimum or exceed maximum levels. Since such low voltage or high voltage levels could cause damage to electrical equipment supplied by the generator, most on-board electrical systems include a manually operable generator disconnect switch whereby the generator can be temporarily disconnected from the electrical load before any change in engine cruise speed is carried out. Occasionally, however, the boat operator fails to or forgets to operate the disconnect switch at the appropriate time with the result that the engine speed change and a high or low voltage condition damages electrical equipment.